1. Field of the Invention
The present invention relates to a collision detecting system for an occupant protector, such as a gas bag designed so that the occupant protector is actuated in case of a collision over a certain high speed to secure the occupant in his seat, and more particularly the present invention relates to a collision detecting system of the type adapted for detecting the deceleration of a vehicle in case of a collision.
2. Description of the Prior Art
Conventional detecting systems of the above type have been usually designed so that the weight adapted to be moved upon occurrence of a deceleration strikes against and closes the normally-open contacts, and a current flows through the contacts to actuate the occupant protector. The contacts are also designed so that they are subjected to a certain elastic deformation to ensure the flow of current through the contacts for a predetermined period of time.
However, the known detecting systems constructed as described above is disadvantageous in that while these systems are effective in collisions of larger vehicles where the detection of the collision can be effected at a relatively slow speed, these systems can hardly be of any practical use in collisions of smaller ones where the detection of the collision must be accomplished within a very short period of time following the actual commencement of the collision. In other words, since the contacts must be subjected to a considerably large elastic deformation to ensure the required holding time of the signal for actuating the occupant protector, the detection of the collision will be delayed and moreover it is impossible to accurately determine the magnitude of the collision to be detected. Another disadvantage is the poor reliability of the system, since the system is subject to malfunctions due to causes such as the formation of an oxide layer on the surface of the contacts due to the fact that the circuit is normally opened in the system.
An exemplary form of the conventional collision detecting systems of the type which have the above-mentioned disadvantages is shown in FIG. 1, and in the arrangement shown in FIG. 1a, in response to a deceleration due to a collision, a weight 2 which is mounted on a spring 1 moves a movable contact 3. The movable contact 3 is provided with a wedge contact piece 4 so that when the contact piece 4 bites into a stationary contact 5, the circuit between an ignitor 6 and a power source 7 is closed to actuate the ignitor 6 of a gas bag. In this case, the ignitor 6 may for example be other actuating means which requires the flow of a considerably large current, and therefore if there is an oxide layer formed on the surface of the stationary contact 5 or the contact piece 4 or if the contact piece 4 is allowed to contact with the stationary contact 5 only slightly, it is impossible to ensure a reduced electric resistance at the contacting points for a sufficiently long period of time. While, for this reason, the contact piece 4 is adapted to bite into the stationary contact 5 to provide the required signal holding time for maintaining a sufficient current flow, this requires a considerable time before the circuit is completely closed after the occurrence of a collision of the vehicle, thus making it impossible to install the system of this type particularly on smaller vehicles.
FIG. 1b is a characteristic diagram showing a typical form of the energizing signal produced in the conventional collision detecting system shown in FIG. 1a. In FIG. 1b, the curve A shows an exemplary form of the collision deceleration waveform with the abscissa representing the time. The curve B shows the current flow through the contacts 3 and 5 of FIG. 1a corresponding to the collision deceleration waveform of the curve A. When a collision occurs at a time t.sub.0, the contacts 3 and 5 come into contact at a time t.sub.1 at which the flow of current is still insufficient, and it is at a time t.sub.2 that the satisfactory final contact is established to achieve a stable conduction state. In other words, the time t.sub.2 - t.sub.1 = t.sub.G is a kind of undetermined factor that arises from the unstable contact between the contacts 3 and 5. Consequently, a considerable time elapses before the flow of current is established between the contacts 3 and 5, thus causing a delay in the detection of the collision. In addition, due to the noise that will be produced by the current flowing before the establishment of the full conduction state, if the system is installed particularly on a smaller vehicle, it is impossible to ensure the positive actuation of the occupant protector. These are phenomena which are bound to happen in the conventional detecting systems.